support I18N (not finished) (thanks takahashim)

Import from  https://github.com/takahashim/mrubysearch/commit/cfaacc6430f39821338fc81a99a523e757d5affa
locale can be changed with URL params like "?locale=en" and stored in sessions (cookies) (thanks takahashim)

Import from  https://github.com/takahashim/mrubysearch/commit/798de545e880c4ce97d96be1f2ec9703cdf780e1